The prediction of a patient outcome has been the goal of physicians for many years. For example, the evaluation of the surface electrocardiogram (ECG), in particular the QRS morphology and ST segment of the heartbeat, is central to the diagnosis, management and prognosis of patients with acute coronary syndromes or ACS. In most cases, clinical care focuses on an examination by a physician of an ECG and any arrhythmias detected on continuous monitoring. Several techniques have been described to measure specific aspects of the electrocardiographic signal and perform relatively complex analyses, including: heart rate variability (HRV), heart rate turbulence (HRT), T-wave alternans (TWA), signal averaged ECG (SAECG), and QT dispersion.
A number of these methods have been shown to provide benefit with respect to identifying high risk patients post ACS. For example, in ACS several studies suggest that HRV alone (both frequency and time domain measures) can be used to predict cardio-vascular mortality in patients who have had a recent myocardial infarction (MI). HRT has also been shown to identify patients at high-risk of death post MI. Both SAECG and TWA can identify patients at increased risk for ventricular arrhythmias post myocardial infarction. In sum, these techniques provide incremental benefit in identifying patients at high risk of subsequent cardiovascular events and may offer insight into pathological changes in the different components of cardiac activation and repolarization.
Many of these techniques focus on specific aspects of the electrocardiogram. T-wave alternans, for example, analyzes beat-to-beat changes in the T-wave amplitude, while ignoring other aspects of the ECG signal, in an attempt to classify patients who are at high risk for future adverse events. Similarly, HRV focuses on beat-to-beat variations in R-R intervals to calculate quantitative estimates of cardiovascular risk. Hence two ECG signals will yield the same calculated HRV measure if they have the same distribution of R-R intervals, regardless of whether the QRS complexes and ST-T wave segments have different morphologies.
This invention relates to an assessment of the entire physiological segmentable signal (for example the entire ECG beat (P wave-to-T wave)) to provide added information that can be used to identify high-risk patient subgroups.